If you put a lab mouse on a diet, cutting the animal’s caloric intake by 30 per cent to 40 per cent, it will live, on average, about 30 per cent longer. The calorie restriction, as the intervention is technically called, can’t be so extreme that the animal is malnourished, but it should be aggressive enough to trigger some key biological changes.

Scientists first discovered this phenomenon in the 1930s, and over the past 90 years it has been replicated in species ranging from worms to monkeys. The subsequent studies also found many of the calorie-restricted animals were less likely to develop cancer and other chronic diseases related to ageing.